1. Field of the Invention
The present invention relates in general to an image projector, and more particularly to an apparatus capable of obtaining a full color by using one LCD as well as effectively cooling the LCD(Liquid Crystal Device).
2. Description of the Conventional Art
Conventionally, for developing a full color by using one projection type LCD, a variety of LCD projectors have been well known in the industry.
Among them, two types of LCD projectors equipped with either a pixel-by color filter or a circular rotating disk color filter will now be explained.
With reference to FIG. 1, a typical LCD projector using a pixel-by color filter, a lamp 1 which is disposed at the inside end portion of the body of a projector for generating parallel light is shown. An ultra violet/infrared ray cut filter 2 for passing only visual rays, while reflecting the ultra violet and infrared rays among the parallel rays which are advanced from the lamp 1, is disposed in front of the lamp 1. A LCD 3 for displaying images is disposed in front of a color filter 4 which is provided for developing a full color by selectively passing only the visual rays from the ultra violet/infrared ray cut filter 2 through a pixel-by color filter. A projection lens 6 for forming an image displayed on the LCD 3 onto a screen 5 is disposed in front of the LCD 3. Here, a lamp cooling fan motor 7 is disposed just behind the lamp 1 for cooling the heat generated due to the strong lighting of the lamp 1. A LCD cooling fan motor 8 is disposed just below the LCD 3 to cool the LCD 3 which is substantially weak to the heat.
However, the LCD projector using the pixel-by color filter, as described above, has disadvantages in that the resolution quality thereof is low because a pixel cell consists of three liquid crystal pixels.
With reference to FIG. 2, a LCD projector using a circular rotating disk color filter according to another embodiment of the conventional LCD projector for resolving the problems of the LCD projector using the pixel-by color filter is shown. Instead of the color filter 4 shown in FIG. 1, a circular rotating disk color filter 4' that is designed to selectively filter light with a bandwidth having a desired wavelength such as Red, Green and Blue is disposed behind the LCD 3.
With reference to FIG. 3, the circular rotating disk color filter 4 is divided into three equal pans at every 120.degree.. Here, the projected image of LCD 3 is reflected onto the surface of the circular rotating disk color filter 4 and shown to occupy the red region.
In FIG. 3, the reference numerals are the same as to those of FIG. 1.
As shown in FIG. 3, the LCD projector using the circular disk rotating color filter 4' is designed to obtain one frame when one rotation thereof is executed, by selectively passing through light with a bandwidth of the visual rays having a predetermined wavelength and dividing the full color in a way of real time.
The image displayed by the circular disk rotating color filter 4' is formed onto a screen 5 through a projection lens 6.
With reference to FIGS. 4A and 4B, while the circular disk rotating color filter 4' rotates at a predetermined speed, a LCD projected image is in one of three parts of Red, Green and Blue is shown therein. Here, one region among Red, Green and Blue where is not completely intervened with another region should be ensured for a high efficiency of the color projection. The best projection efficiency angle defined as a1-a2 angle is 30.degree. which is obtained from a formula `a1-a2.` As a result, the conventional circular disk rotating color filter 4' rotates as having a projection efficiency of 30.degree..
In addition, the conventional circular disk rotating color filter 4' requires both a fan motor 4 for cooling the lamp 1 and a LCD cooling fan motor 8 for cooling the LCD 3.
The LCD projector using the conventional circular disk rotating color filter has an advantage of maintaining a resolution as much as the number of pixels while obtaining a color by using one pixel LCD 3 since each pixel can be a picture shell of the LCD 3. However, it requires some additional apparatuses: a lamp cooling fan motor 7 for cooling the lamp 1 and the LCD cooling fan motor 8 for cooling a LCD 3, making the volume thereof large, since the circular disk rotating color filter 4' should be made so that its radius is equal to or greater than the diagonal length of the LCD 3. In addition, when a horizontal and vertical length ratio of the LCD 3 needs to be 16:9 in case of a HDTV(High Definition Television), the size of the disk should be even larger since the size of the LCD 3 should fully fit onto one of the Red, Green and Blue regions.